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Low fin tube manufacturing process

Low-fin tubes are generally machined to form fins with a certain height, a certain distance, and a certain thickness on the outer surface of the smooth tube. Finned tubes are mostly used in air-conditioning condensers and heat exchange elements of evaporators, and low-finned tubes are often used in condensers.

There are two important parameters to describe the performance of low finned tubes, namely, fin ratio β Fin efficiency η。 Winged comparison“ β” The definition can be derived from the formula: β = Total surface area of finned tube / surface area of original smooth tube; β The larger it is, the more severe the expansion of the heat exchange area of the finned tube is, and its heat exchange performance is also enhanced. In the heat exchange process of finned tube, it is assumed that the temperature of the fluid in the tube is higher than that outside the tube, and the heat is transferred outward in the form of heat conduction from the fin root along the fin height through the tube wall. At the same time, the fins also conduct convective heat exchange with the surrounding fluid, resulting in the gradual decrease of the fin temperature along the fin height direction.

Low-fin tubesLow fin tube manufacturing process

The low-fin tube is processed and produced by the rolling method (three-roll skew rolling). Its working principle is: the smooth tube is lined with a mandrel. The hole type composed of the groove and the core rod is gradually processed with fins on the outer surface. In order to be more conducive to fin forming, the rolling piece adopts three stages of biting, rolling and shaping during the deformation process to make the processed fin complete, smooth and regular. The fin tube produced by this method is based on the base tube and The outer fin is an organic whole, so there is no contact thermal resistance loss and electric corrosion problems, and it has good heat transfer efficiency and strong resistance to deformation.

Low fin tube  structural parameters of the low-fin tube are mainly the inner diameter and outer diameter of the fin tube, the wall thickness of the fin tube, the fin pitch, the thickness of the fin, and the height of the fin.

It is generally used where the heat supply coefficient inside the tube is more than one time larger than the heat supply coefficient outside the tube. The most typical application is an oil heat exchanger. For condensation and boiling outside the tube, due to the effect of surface tension, it also has a better heat transfer enhancement effect. Its processing has been industrialized, and the design correlation formula has been verified in Changling Refinery and other factories. 

(1) As far as the heat transfer effect is concerned, the primary and secondary relationship of the various structural parameters of the low fin tube is: fin pitch → fin height → fin thickness, and the fin pitch is within 1~2 mm. The thermal performance increases with the increase of the fin pitch. When the fin pitch exceeds 2mm, the heat transfer performance increases and decreases; the heat transfer performance decreases with the increase of the fin thickness, and increases with the increase of the fin height.

(2) The pressure drop outside the fin tube is significantly affected by the fin height. The pressure drop increases geometrically with the increase of the fin height. The fin pitch also has a significant effect on the pressure drop. The pressure drop increases with the fin pitch. When it becomes larger, the pressure drop is hardly affected by the wing thickness.

(3) When the flow rate of the fluid inside and outside the tube increases, the heat exchange rate and pressure drop of the finned tube also increase. When the flow rate of the fluid outside the tube increases, the increase in pressure drop is significantly greater than the increase in heat exchange rate. When the flow rate increases, the pressure drop outside the tube remains unchanged, and the increase in the pressure drop inside the tube is smaller.

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